TinyXML is a simple, small, minimal, C++ XML parser that can be easily integrating into other programs. It reads XML and creates C++ objects representing the XML document. The objects can be manipulated, changed, and saved again as XML.
*Please Note* that TinyXML development has stopped and all development has moved to TinyXML-2. TinyXML-2 is available at https://github.com/leethomason/tinyxml2

Object Oriented Input System (OIS) is meant to be a cross platform, simple solution for using all kinds of Input Devices (Keyboards, Mice, Joysticks, etc) and feedback devices (e.g. force feedback). Written in C++ using Object Oriented Design pattern

GLUI is a GLUT-based C++ user interface library which provides controls such as buttons, checkboxes, radio buttons, and spinners to OpenGL applications. It is window-system independent, using GLUT or FreeGLUT.